On Fri, 1 Oct 2004, Tim Maher wrote:
> On Fri, Oct 01, 2004 at 08:25:02AM -0700, DeRykus, Charles E wrote:
> >
> > But, as we've seen Joel's post, the effects of a "list in
> > scalar context" in a different may altogether different and
> > unexpected... ie, while () ... gets parsed as for (;;).
> > Charles DeRykus
>> I've been skimming this thread, but having trouble with a fundamental
> element of the discussion.
>> Specifically, what qualifies
>> while () { statement; }
>> as having /anything/ to do with the conceptually understandable (albeit
> technically non-existent) "list in scalar context"?
Good point, it has nothing to do with "list in a scalar context".
while() of course just checks the conditional in parens for truth, and the
parens are syntax, not a list. The reason I brought empty list into the
discussion is that I was burned once a year or two ago with an empty list
issue, where it didn't behave as I expected. I think it was with a regex
match, but unfortunately I can't remember exactly what the situation was.
:-) I wanted to point it out just as a debugging thing I tried.
John pointed out:
That is working for the same reason that
for ( ;; ) { ... }
works in Perl as well as in C where Perl inherited it from.
I guess that's a good enough explanation, but it still seems to me like
while () {
}
should intuitively evaluate to false. I'll get over it. Or at least
memorize it.
Btw, if you really want to use while() without the parens, you could do:
do {
print "hello world\n";
} while $x++ < 3;
# not to my tastes, but tmtowtdi...
Joel
> Or, for that matter, the parens in while's close relative:
>> if () { statement; }
>> AFAIK, those parens after the keywords are *required elements of
> syntax* that have nothing to do with the kind of "list formation"
> effect that people associate with expressions like:
> @stuff=(1,2,3);
> and
> @stuff=(); # empty list
>> It seems to me that earlier posts are equating the parens in
> "while ()..." to those in my empty list example above, which
> conflicts with my interpretation that they are merely
> syntactic elements after "while".
>> If they're /not/ syntactic, why can't we write code like this?
> while $foo { statement; }
> while @foo { statement; }
> or
> if 1 { statement; }
>> (And that code doesn't compile; I checked!)
>> I'll readily admit that I, like many JAPHs, have some of my own
> ways of thinking about Perl that make it easier for me to use, and
> to teach, and that usually serve me quite well -- despite their
> technically being over-simplifications of Perl's (twisted)
> reality. 8-}
>> As a case in point, I offer the widespread notion that parens
> function as "list constructors" in expressions like
> "@array=(1,2)" and "print (1,2)", which is tremendously useful,
> despite being less than a perfectly accurate representation of
> how those expressions are actually parsed and evaluated, IIRC.
> (What's the real story? Is it that the comma operator in list
> context returns all the expressions, so the parens are just there
> for reasons of precedence in the case of an assignment?)
>> Surely, even in Perl, there are some elements of basic syntax
> that can be trusted to have concrete meanings -- like while's
> parens; aren't there? 8-}
>> *--------------------------------------------------------------------------*
> | Tim Maher, CEO (206) 781-UNIX (866) DOC-PERL (866) DOC-UNIX |
> | tim(AT)Consultix-Inc.Com http://TeachMePerl.Comhttp://TeachMeUnix.Com |
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